The Renin-Angiotensin system (RAS) regulates blood pressure and cardiovascular homeostasis. During pregnancy the RAS participates in processes such as trophoblast proliferation and migration and regulates placental vascular tone. Human studies have revealed that the uteroplacental RAS becomes dysregulated in pregnancy complications like recurrent miscarriage (fetal loss), intrauterine growth restriction (IUGR) and pre-eclampsia (PE). In addition, the maternal RAS becomes dysregulated in PE which is characterized by maternal hypertension and proteinuria. We have recently discovered that the Brown Norway (BN) rat model of placental insufficiency present uteroplacental and maternal RAS dysregulation, characterized by higher Angiotensin II, Angiotensin I-converting enzyme (ACE) and Angiotensin II receptor 1 (AGTR1) expression. In addition, late-pregnant BN dams were hypertensive and proteinuric. The isogenetic BN rat possesses an ACE polymorphism that is similar to the human ACE D/D polymorphism that leads to increased ACE activity. For this reason we hypothesize that increased RAS activation in the BN rat has an important role in placental insufficiency and PE. We will utilize the BN rat as a model of placental insufficiency linked to ACEhigh genotype (similar to the human ACE D/D genotype) and the Lou rat (L) as a model of normal pregnancy linked to ACElow genotype (similar to the human ACE I/I genotype). The specific aims are: 1) to determine whether increased uteroplacental RAS activation in BN rats is necessary to observe placental insufficiency, and 2) to determine whether increased maternal RAS activation in BN rats is necessary to induce PE. We will investigate the uteroplacental and maternal RAS in four study groups: i.e., BBN x @BN, BBN x @L, L mother with BN fetus and BN mother with L fetus at various developmental stages. The expression of RAS members will be determined by real-time PCR and immunoblotting. ACE and ACE2 enzymatic activity and Angiotensin II and 1-7 tissue levels will be assessed by EIA. To determine the role of AGTR1 in uteroplacental blood flow and pregnancy outcomes of the BN rat, we will use an AGTR1 antagonist (Losartan) in additional four groups (BN-vehicle, BN-losartan, L-vehicle and L- Losartan). Maternal blood pressure, proteinuria, and the dimerization status of the AGTR1a will be assessed. This proposal will unravel the RAS ontogeny in rat models of normal and inadequate placental development. In addition, the outcomes of this proposal will shed light into the role of RAS genetics in pregnancy outcomes and will provide the scientific community with a novel animal model to study the genetics of placental insufficiency and PE.